Battery with wound electrode group and positive and negative electrode insulating covers

ABSTRACT

According to one embodiment, there is provided a battery. The battery includes a metallic outer can, a wound electrode group, a positive electrode-lead, a negative electrode-lead, a positive electrode insulating cover, and a negative electrode insulating cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims the benefitof priority under 35 USC § 120 from U.S. application Ser. No.13/165,011, filed Jun. 21, 2011, which is based upon and claims thebenefit of priority 35 USC § 119 from Japanese Patent Applications No.2010-141007, filed Jun. 21, 2010; No. 2010-223219, filed Sep. 30, 2010;and No. 2011-082952, filed Apr. 4, 2011, the entire contents of all ofwhich are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a battery.

BACKGROUND

Since lithium ion secondary batteries have high energy densities, theyare expected to be used for power sources for electric cars, hybridvehicles, electric motorcycles, forklifts, and the like. In order toobtain an electric power source having a larger capacity, an assembledbattery has been developed by connecting a plurality of batteries.

The lithium ion secondary battery includes a metallic outer can, a woundelectrode group accommodated in the outer can, leads, and a metallic lidattached to an opening portion of the outer can. For example, the lid iswelded to the opening portion of the outer can. A positive electrodecurrent-collecting tab is provided at one end in a winding axisdirection of the wound electrode group. A negative electrodecurrent-collecting tab is provided at the other end thereof. Thepositive electrode current-collecting tab is connected with a positiveelectrode-lead. The negative electrode current-collecting tab isconnected with a negative electrode-lead. The lid is equipped with apositive electrode terminal and a negative electrode terminal. Theseterminals are fixed to the lid by caulking. For example, a gasketbecomes caught between these terminals and the lid, so that theterminals are insulated from the lid and the outer can. The positive andnegative electrode-leads connected with the current-collecting tabs arerespectively connected to the terminal of the positive electrode and theterminal of the negative electrode.

When the current-collecting tabs or the leads come into contact with theouter can of the battery, and in particular, in a case where it is anassembled battery, the outer can gets a high voltage, and there is thepossibility of increasing danger of electric leak and electric shock toa person. Accordingly, a structure for insulating the outer can from thecurrent-collecting tabs and the leads has been considered. However, in acase where vibration, shock, or the like is applied to the battery,there is the possibility that the current-collecting tabs and the leadsmay come into contact with the outer can. Alternatively, in a case wherethe leads are disconnected from the current-collecting tabs of theelectrode group due to, e.g., vibration, shock, or the like, the leadsmay come into contact with the electrode group, and there is thepossibility of causing short circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an external of a rectangularsecondary battery according to a first embodiment;

FIG. 2 is an exploded perspective view illustrating the battery of FIG.1;

FIG. 3 is an exploded perspective view illustrating an electrode groupused for the battery of FIG. 1;

FIG. 4 is a cross sectional view illustrating a cross section takenalong line IV-IV of FIG. 2 when the cross section is seen from adirection of an arrow;

FIG. 5 is a figure illustrating a negative electrode insulating coverused in the battery according to the first embodiment;

FIG. 6 is a perspective view illustrating a step for inserting theelectrode group of the battery of FIG. 1 into an outer can;

FIG. 7 is a cross sectional view illustrating a cross section takenalong line VII-VII of FIG. 6 when the cross section is seen from adirection of an arrow;

FIG. 8 is a perspective view illustrating a first modification of aninsulating cover used for the battery according to the first embodiment;

FIG. 9 is a perspective view illustrating how an electrode group of abattery using the insulating cover of FIG. 8 is received in an outercan;

FIG. 10 is a perspective view illustrating a second modification of aninsulating cover used for the battery according to the first embodiment;

FIG. 11 is a perspective view illustrating an insulating cover used fora battery according to a second embodiment;

FIG. 12 is a perspective view illustrating a first modification of theinsulating cover used for the battery according to the secondembodiment;

FIG. 13 is a perspective view illustrating a second modification of theinsulating cover used for the battery according to the secondembodiment;

FIG. 14 is a perspective view illustrating a third modification of theinsulating cover used for the battery according to the secondembodiment;

FIG. 15 is a perspective view illustrating a fourth modification of theinsulating cover used for the battery according to the secondembodiment;

FIG. 16 is a perspective view illustrating a fifth modification of theinsulating cover used for the battery according to the secondembodiment;

FIG. 17 is an exploded perspective view illustrating a rectangularsecondary battery according to a third embodiment; and

FIG. 18 is a perspective view illustrating a modification of theinsulating cover used for the battery according to the third embodiment.

DETAILED DESCRIPTION

A battery according to an embodiment will be hereinafter explained indetail.

The battery according to the embodiment comprises a metallic outer can,a wound electrode group accommodated in the outer can in a directionperpendicular to a winding axis, wherein a wound positive electrodecurrent-collecting tab is provided at one end of the wound electrodegroup, and a wound negative electrode current-collecting tab is providedat the other end of the wound electrode group, a positive electrode-leadconnected to the positive electrode current-collecting tab, a negativeelectrode-lead connected to the negative electrode current-collectingtab, a metallic lid comprising a positive electrode terminal and anegative electrode terminal and being attached to an opening portion ofthe outer can, a positive electrode insulating cover engaged with oneend portion including the positive electrode current-collecting tab ofthe wound electrode group, and a negative electrode insulating coverengaged with the other end portion including the negative electrodecurrent-collecting tab of the wound electrode group. The positiveelectrode-lead comprises a connection portion connected to the positiveelectrode terminal and first and second sandwiching portions extendingfrom the connection portion to the wound electrode group in thedirection perpendicular to the winding axis to sandwich the woundpositive electrode current-collecting tab. The negative electrode-leadcomprises a connection portion connected to the negative electrodeterminal and first and second sandwiching portions extending from theconnection portion to the wound electrode group in the directionperpendicular to the winding axis to sandwich the wound negativeelectrode current-collecting tab. The positive electrode insulatingcover comprises a U-shaped member having first and second sidewallsfacing each other, a back surface member, and a sandwiching member forsandwiching the first sandwiching portion of the positive electrode-leadand the wound positive electrode current-collecting tab portion facingthe first sandwiching portion and sandwiching the second sandwichingportion of the positive electrode-lead and the positive electrodecurrent-collecting tab portion facing the second sandwiching portion.The negative electrode insulating cover comprises a U-shaped memberhaving first and second sidewalls facing each other, a back surfacemember, and a sandwiching member for sandwiching the first sandwichingportion of the negative electrode-lead and the wound negative electrodecurrent-collecting tab portion facing the first sandwiching portion andsandwiching the second sandwiching portion of the negativeelectrode-lead and the negative electrode current-collecting tab portionfacing the second sandwiching portion.

(First embodiment)

The embodiment will be hereinafter explained with reference to drawings.FIGS. 1 and 2 show a sealed rectangular non-aqueous electrolytesecondary battery 20 as an example of a non-aqueous electrolytesecondary battery. The battery 20 comprises an outer can 1, aflat-shaped wound electrode group 2, a positive electrode-lead 3, anegative electrode-lead 4, a positive electrode insulating cover 25, anda negative electrode insulating cover 26, and a lid 5.

For example, the outer can 1 is formed in a rectangular tube shapehaving a bottom, and is made of metal such as aluminum, aluminum alloy,iron, and stainless steel. The wound electrode group 2 is accommodatedin a direction perpendicular to a winding axis in the outer can 1.

A positive electrode current-collecting tab 8 a is provided at one endof the wound electrode group 2. A negative electrode current-collectingtab 9 a is provided at the other end thereof. FIG. 3 is an explodedperspective view illustrating the wound electrode group 2. The positiveelectrode 8 comprises a positive electrode current-collecting body 8 cin a belt shape made of, e.g., a metal foil and a positive electrodeactive material layer 8 b formed on one surface or both surfacesthereof. The positive electrode active material layer 8 b is formed suchthat a region having a certain width (non-coated portion) remains at oneend side in a longitudinal direction of the belt-shaped positiveelectrode current-collecting body 8 c. This non-coated portion is aportion in which the positive electrode current-collecting body 8 c isexposed, and this serves as the positive electrode current-collectingtab 8 a. Likewise, the negative electrode 9 comprises a negativeelectrode current-collecting body 9 c in a belt shape made of, e.g., ametal foil and a negative electrode active material layer 9 b formed onone surface or both surfaces thereof. The negative electrode activematerial layer 9 b is formed such that a region having a certain width(non-coated portion) remains at the other end side in a longitudinaldirection of the belt-shaped negative electrode current-collecting body9 c (at the side opposite to the one end of the positive electrode 8).This non-coated portion is a portion in which the negative electrodecurrent-collecting body 9 c is exposed, and this serves as the negativeelectrode current-collecting tab 9 a.

The positive electrode 8 and the negative electrode 9 are stackedalternately with the belt-shaped separators 10 a, 10 b. At thisoccasion, the positive electrode current-collecting tab 8 a is providedat one end side in the winding axis direction, and the negativeelectrode current-collecting tab 9 a is provided at the other end side.The separator 10 a stacked below the positive electrode 8 is arrangedsuch that one end of the separator 10 a in the longitudinal directionthereof is located at an inner side with respect to the end portion ofthe positive electrode 8 at the side of the positive electrodecurrent-collecting tab. Accordingly, the positive electrodecurrent-collecting tab 8 a protrudes from the positive electrode activematerial layer 8 b, the negative electrode active material layer 9 b,and the separator 10 a, which constitute the wound electrode group 2.The separator 10 a is arranged such that the other end of the separator10 a in the longitudinal direction thereof is located at an outer sidewith respect to the other end of the positive electrode 8. The separator10 b sandwiched between the positive electrode 8 and the negativeelectrode 9 is arranged such that one end in the longitudinal directionis located at an inner side with respect to the end portion of thenegative electrode 9 at the side of the negative electrodecurrent-collecting tab. Accordingly, the negative electrodecurrent-collecting tab 9 a protrudes from the positive electrode activematerial layer 8 b, the negative electrode active material layer 9 b,and the separator 10 b, which constitute the wound electrode group 2.The separator 10 b is arranged such that the other end of the separator10 b in the longitudinal direction thereof is located at an outer sidewith respect to the other end of the negative electrode 9.

The flat-shaped wound electrode group 2 is formed by stacking andwinding the separator 10 a, the positive electrode 8, the separator 10b, and the negative electrode 9 and subsequently pressing them.

As shown in FIG. 2 most clearly, the wound electrode group 2 is attachedby an insulating tape 30. The insulating tape 30 covers the outermostperiphery of the wound electrode group 2 except for thecurrent-collecting tab, so as to insulate the outermost periphery exceptfor the current-collecting tab. The insulating tape 30 may be wound oneor more times.

The metallic lid 5 is fixed, in an air tight manner, to the openingportion of the outer can 1 by, e.g., welding. The positive electrodeterminal 6 and the negative electrode terminal 7 fixed to the lid 5 bycaulking. The insulating gaskets 14, 15 become caught between theseterminals and the lid. The positive electrode terminal 6 and thenegative electrode terminal 7 respectively protrude from the backsurface of the lid 5 to the inside of the outer can 1. The method forfixing the positive electrode terminal 6 and the negative electrodeterminal 7 comprises not only caulking with the insulating gaskets 14,15 but also hermetic seal using glass.

The positive electrode-lead 3 comprises a connection plate 3 a, apenetrating hole 3 b, and first and second sandwiching strips 3 c, 3 d.The connection plate 3 a is a connection portion connected to thepositive electrode terminal 6. The penetrating hole 3 b is formed in theconnection plate 3 a. The first and second sandwiching strips 3 c, 3 dare sandwiching portions branched off from the connection plate 3 a andextending to the wound electrode group 2 in a direction perpendicular tothe winding axis. The connection plate 3 a is in contact with the backsurface of the lid 5 at the portion of the positive electrode terminal 6with an insulating sheet (not shown) interposed therebetween, and thepositive electrode terminal 6 protruding from the back surface of thelid 5 is fixed with the penetrating hole 3 b by caulking.

The positive electrode current-collecting tab 8 a is sandwiched by thefirst and second sandwiching strips 3 c, 3 d of the positiveelectrode-lead 3 from the direction perpendicular to the winding axis,and the first and second sandwiching strips 3 c, 3 d and the positiveelectrode current-collecting tab 8 a are connected by, e.g., welding.

Likewise, the negative electrode-lead 4 comprises a connection plate 4a, a penetrating hole 4 b, and first and second sandwiching strips 4 c,4 d. The connection plate 4 a is a connection portion connected to thenegative electrode terminal 7. The penetrating hole 4 b is formed in theconnection plate 4 a. The first and second sandwiching strips 4 c, 4 dare sandwiching portions branched off from the connection plate 4 a andextending to the wound electrode group 2 in the direction perpendicularto the winding axis. The connection plate 4 a is in contact with theback surface of the lid 5 at the portion of the negative electrodeterminal 7 with an insulating sheet (not shown) interposed therebetween,and the negative electrode terminal 7 protruding from the back surfaceof the lid 5 is fixed with the penetrating hole 4 b by caulking.

The negative electrode current-collecting tab 9 a is sandwiched by thefirst and second sandwiching strips 4 c, 4 d of the negativeelectrode-lead 4 from the direction perpendicular to the winding axis,and the first and second sandwiching strips 4 c, 4 d and the negativeelectrode current-collecting tab 9 a are connected by, e.g., welding.

It should be noted that the above welding may be carried out accordingto methods such as resistance welding and ultrasonic welding.

The leads of the positive/negative electrodes having the above structureenable the first and second sandwiching strips to be arranged equallywith respect to the current-collecting tabs. Further, since there aretwo (first and second) sandwiching strips, the current collectiondistance is short. This improves the balance of current collection, andimproves the efficiency of current collection. Further, in the leadshaving the first and second sandwiching strips as explained above, heatis less likely to be concentrated at a joint portion between thecurrent-collecting tab and the first and second sandwiching strips andat the leads themselves, and therefore, even in a case where a largecurrent is passed therethrough, good electrical characteristics can bemaintained.

The leads of the positive/negative electrodes and the current-collectingtabs of the positive/negative electrodes may be connected while thecurrent-collecting tabs are partially fixed with fixing members as shownin FIG. 2. In other words, the positive electrode current-collecting tab8 a is fixed with the fixing member 11, and the negative electrodecurrent-collecting tab 9 a is fixed with the fixing member 12.

The fixing members of the positive/negative electrodes have the sameshape as each other, and they are arranged symmetrically whencurrent-collecting tabs of the positive/negative electrodes are fixed.Therefore, the fixing member 12 for fixing the negative electrodecurrent-collecting tab 9 a will be explained in detail as an examplewith reference to FIG. 4. Since the negative electrodecurrent-collecting tab 9 a is wound, it is made of a bundle in a shapeof hollow prolate ellipsoid in which a plurality of current-collectingtabs are overlapped. The fixing member 12 has first and second holdingunits 12 a, 12 b and a coupling unit 12 c. The first and second holdingunits 12 a, 12 b are in a U shape, and are respectively engaged with twoportions facing each other in the minor axis direction of the hollowprolate ellipsoid in proximity to a central portion of the negativeelectrode current-collecting tab 9 a, thus binding the negativeelectrode current-collecting tab 9 a. The coupling unit 12 c is in aflat shape, and couples the first and second holding units 12 a, 12 bwith each other within the ellipsoid formed by the negative electrodecurrent-collecting tab 9 a. The negative electrode current-collectingtab 9 a is connected with the first and second holding units 12 a, 12 bby, e.g., welding.

The negative electrode current-collecting tab 9 a attached with thefixing member 12 is sandwiched by the first and second sandwichingstrips 4 c, 4 d of the negative electrode-lead 4. Therefore, as shown inFIG. 4, the first sandwiching strip 4 c is in contact with the externalsurface of the first holding unit 12 a, and the second sandwiching strip4 d is in contact with the external surface of the second holding unit12 b. In these contact portions, the first and second sandwiching strips4 c, 4 d and the first and second holding units 12 a, 12 b are connectedby, e.g., welding.

It should be noted that the above welding may be carried out accordingto methods such as resistance welding and ultrasonic welding.

The thicknesses of the first and second holding units 12 a, 12 b aredesirably thinner than the thicknesses of the first and secondsandwiching strips 4 c, 4 d of the leads 4. When the thicknesses of thefirst and second holding units 12 a, 12 b are reduced, they can beeasily fixed to predetermined two portions of the negative electrodecurrent-collecting tab 9 a. In addition, this facilitates couplingbetween the negative electrode current-collecting tab 9 a, the first andsecond holding units 12 a, 12 b, and the first and second sandwichingstrips 4 c, 4 d of the leads. Further, this can reduce the resistance atthe joint portion between the first and second holding units 12 a, 12 band the negative electrode current-collecting tab 9 a.

It should be noted that a length between the first sandwiching strip 4 cand the second sandwiching strip 4 d of the lead 4 is defined as beingshorter than a length T in a thickness direction of the wound electrodegroup 2.

The fixing member 12 is made of a metallic conductive material.Therefore, the negative electrode 9 of the wound electrode group 2 iselectrically connected to the lead 4 via the fixing member 12, and isfurther electrically connected to the negative electrode terminal 7 ofthe lid 5 via the lead 4.

Using the above fixing member, the thickness of the portion of thecurrent-collecting tab of the wound electrode group 2 is reduced, sothat a space for arranging the lead within the outer can be ensured.Since it is not necessary to newly arrange a space for the lead, thisimproves the energy density of the battery 20.

It should be noted that the fixing member may have only first and/orsecond holding units, and may have no coupling unit. The first andsecond holding units are in a U shape.

The structure of the fixing members 11 and the fixing form of thepositive electrode current-collecting tab 8 a with the fixing members 11are the same as those of the above fixing member 12 and the negativeelectrode current-collecting tab 9 a. It should be noted that the fixingmembers 11 comprise U-shaped holding units 11 a, 11 b and a flatcoupling unit 11 c.

Insulating covers 25, 26 of the positive/negative electrodes arerespectively engaged with both end portions including thecurrent-collecting tabs of the wound electrode group 2 sandwiched by thefirst and second sandwiching strips of the leads of thepositive/negative electrodes, and the insulating covers 25, 26 coverthese sandwiching strips and the current-collecting tabs.

The current-collecting tabs of the positive/negative electrodes and theinsulating covers of the positive/negative electrodes covering the leadssandwiching the current-collecting tabs have the same shape as eachother and are arranged symmetrically. Therefore, the negative electrodeinsulating cover 26 covering the negative electrode current-collectingtab 9 a and the first and second sandwiching strips 4 c, 4 d of thenegative electrode-lead 4 are explained in detail as an example withreference to FIGS. 2 and 5.

As shown in FIGS. 2 and 5, the negative electrode insulating cover 26comprises a U-shaped member 26 a, a back surface member 26 d, and asandwiching member. The U-shaped member 26 a has first and secondsidewalls 26 b, 26 c facing each other. The back surface member 26 d isintegrated with the back surface of the U-shaped member 26 a. Thesandwiching member sandwiches the negative electrode current-collectingtab 9 a and the first and second sandwiching strips 4 c, 4 d of thenegative electrode-lead 4. A lower portion of the U-shaped member 26 ais bent, and an upper portion thereof is open. The U-shaped member 26 ais made such that the side opposite to the back surface member 26 d isalso open.

The sandwiching member comprises first and second rectangular thickportions 26 e, 26 f respectively arranged in proximity to centralportions of the first and second sidewalls 26 b, 26 c and a rectangularprotruding portion 26 g arranged on the back surface member 26 d. Theprotruding portion 26 g is provided with predetermined clearances (afirst clearance 26 x, a second clearance 26 y) from the first and secondthick portions 26 e, 26 f. The protruding portion 26 g and the first andsecond thick portions 26 e, 26 f are in a lengthwise direction of thefirst and second sidewalls 26 b, 26 c, and have the same length. Thelength of protrusion of the protruding portion 26 g from the backsurface member 26 d is less than the width of the sidewalls 26 b, 26 cof the U-shaped member 26 a. It should be noted that the protrudingportion 26 g may be in a hollow shape.

The negative electrode insulating cover 26 is engaged with an endportion including the negative electrode current-collecting tab 9 a ofthe wound electrode group 2. Accordingly, the bent lower portion of theU-shaped member 26 a is in contact with the lower portion of thenegative electrode current-collecting tab 9 a, and the first and secondsidewalls 26 b, 26 c of the U-shaped member 26 a are in contact with thefirst and second sandwiching strips 4 c, 4 d of the negativeelectrode-lead 4 sandwiching the negative electrode current-collectingtab 9 a.

As shown in FIGS. 6 and 7 (in which the fixing member 12 is attached),the negative electrode current-collecting tab 9 a bound and fixed by thefirst holding unit 12 a and the first sandwiching strip 4 c of thenegative electrode-lead 4 in contact with the outer surface of the firstholding unit 12 a are inserted into and sandwiched by the firstclearance 26 x between the first thick portion 26 e and the protrudingportion 26 g of the sandwiching member. On the other hand, the negativeelectrode current-collecting tab 9 a bound and fixed by the secondholding unit 12 b and the second sandwiching strip 4 d of the negativeelectrode-lead 4 in contact with the outer surface of the second holdingunit 12 b are inserted into and sandwiched by the second clearance 26 ybetween the second thick portion 26 f and the protruding portion 26 g ofthe sandwiching member. In other words, when the first holding unit 12 aand the first sandwiching strip 4 c are inserted into the firstclearance 26 x, the first holding unit 12 a and the first sandwichingstrip 4 c are sandwiched by elastic force provided by the first thickportion 26 e and the protruding portion 26 g forming the first clearance26 x. Likewise, when the second holding unit 12 b and the secondsandwiching strip 4 d are inserted into the second clearance 26 y, thesecond holding unit 12 b and the second sandwiching strip 4 d aresandwiched by elastic force provided by the second thick portion 26 fand the protruding portion 26 g forming the second clearance 26 y.

The negative electrode insulating cover is preferably integrally moldedfrom resin, and is formed using an insulating material. Examples ofmaterials may include polypropylene, polyimide, polyphenylene sulfide(PPS), and polyester (PET). In particular, it is desirable to be formedfrom polypropylene in view of heat resistance, insulation, and cost.

The positive electrode insulating cover 25 has the same structure as thenegative electrode insulating cover 26. The relationship between thepositive electrode insulating cover 25 and the end portion of the woundelectrode group 2 including the positive electrode current-collectingtab 8 a is the same as the relationship between the negative electrodeinsulating cover 26 and the end portion of the wound electrode group 2including the negative electrode current-collecting tab 9 a. Thepositive electrode insulating cover 25 comprises a U-shaped member 25 a,a back surface member 25 d, and a sandwiching member. The U-shapedmember 26 a has first and second sidewalls 25 b, 25 c facing each other.The back surface member 25 d is integrated with the back surface of theU-shaped member 25 a. The sandwiching member sandwiches the positiveelectrode current-collecting tab 8 a and the first and secondsandwiching strips 3 c, 3 d of the positive electrode-lead 3. Thesandwiching member comprises first and second rectangular thick portions25 e, 25 f respectively arranged in proximity to central portions of thefirst and second sidewalls 25 b, 25 c and a rectangular protrudingportion 25 g arranged on the back surface member 25 d. The protrudingportion 25 g is provided with predetermined clearances (a firstclearance 25 x, a second clearance 25 y) between the first and secondthick portions 25 e, 25 f.

In the battery according to the embodiment as described above, thecurrent-collecting tabs and the leads are covered with the insulatingcovers made of the insulating material. Therefore, the wound electrodegroup 2 is insulated from the outer can 1. Further, since the jointportion between the current-collecting tab and the lead is sandwiched bythe sandwiching member of the insulating cover, the current-collectingtab and the lead are less likely to be disconnected from each other evenwhen vibration or shock is applied to the battery. Therefore, thisprevents short-circuit caused by the lead coming into contact with thewound electrode group 2. In addition, this makes it less likely todetach the insulating cover itself from the end portion of the woundelectrode group 2. In addition, the insulating cover reduces movement ofthe wound electrode group 2 within the battery. This prevents thecurrent-collecting tab from being deformed or damaged, and disconnectedfrom the lead. Therefore, this more reliably ensures insulation betweenthe leads, the current-collecting tabs, and the outer can.

As shown in FIGS. 6 and 7, the positive/negative electrodes insulatingcovers 25, 26 engaged with the end portions of the wound electrode group2 are fixed to the insulating tape 30 using insulating cover fixingtapes 27. In order to prevent increase of the thickness, design ispreferably made such that the positive/negative electrodes insulatingcovers 25, 26 do not overlap the insulating tape 30. Alternatively,design may be made such that the positive/negative electrodes insulatingcovers 25, 26 overlap the insulating tape 30, so that the insulatingcovers are fixed without using the insulating cover fixing tape 27.

Since the wound electrode group 2 is covered with the insulating tape 30and the insulating cover 25, the wound electrode group 2 can be easilyinserted into the outer can 1. This configuration prevents the woundelectrode group 2 from being damaged when it is inserted into the outercan 1. Since insertion is easy, the electrode group can be made in asize close to the internal size of the outer can 1, which improves thevolumetric efficiency. Insulation of the wound electrode group 2 isensured only by the insulating cover 25 and the insulating tape 30, andtherefore, the number of components needed for insulation can bereduced, and the volume of the insulating members can be reduced. Thiscan increase the volume of the wound electrode group 2 that can beaccommodated in the outer can 1, and can improve the volumetricefficiency.

Resins usable as a base material of the insulating tape 30 can be chosenfrom, for example, polyester (PET), polyimide, polyphenylene sulfide(PPS), and polypropylene.

For example, the lid 5 is made of metal such as aluminum, aluminumalloy, iron, and stainless steel. The lid 5 and the outer can 1 arepreferably formed from the same type of metal.

After the lid 5 is fixed to the outer can 1, electrolyte (not shown) isinjected through an inlet 28 provided in the lid 5. After the injection,the flat electrode group 2 is impregnated with the electrolyte.

It should be noted that the sandwiching member of the insulating coveris not limited to the shape protruding to the inner side from thesidewall of the U-shaped member. For example, a sandwiching memberhaving a recessed portion may be used so that the fixing member and thesandwiching strips of the lead engaged with the fixing member areinserted into the recessed portion.

Subsequently, a first modification of the insulating cover (e.g.,negative electrode insulating cover 26) is shown in FIG. 8. In thismodification, the same configurations as those of the above insulatingcover 26 are denoted with the same reference numerals as those of FIG.5, and description thereabout is omitted.

The insulating cover 26 as shown in FIG. 8 has an extending portion 26 hprovided at a bent portion of a lower of a U-shaped member 26 a, and theextending portion 26 h extends in a direction opposite to the backsurface member 26 d. Further, the extending portion 26 h has one or morechannel grooves 26 i extending in parallel with the extending portion 26h.

Since the wound electrode group 2 is held by the extending portion 26 h,as shown in FIG. 9, the insulating cover 26 according to thismodification is fixed to the wound electrode group 2 more rigidly.Further, the channel grooves 26 i also function as inflow paths ofelectrolyte. When the wound electrode group 2 is accommodated in theouter can 1, and the electrolyte is injected, the electrolyte flows intothe wound electrode group 2 via the channel grooves 26 i. This canaccelerate impregnation of the electrolyte into the wound electrodegroup 2.

Subsequently, a second modification of the insulating cover (e.g.,negative electrode insulating cover 26) is shown in FIG. 10. In thismodification, the same configurations as those of the above insulatingcover 26 are denoted with the same reference numerals as those of FIG.5, and description thereabout is omitted.

In the negative electrode insulating cover 26 as shown in FIG. 10, thesandwiching member comprises first and second rectangular thick portions26 e, 26 f respectively arranged in proximity to central portions of thefirst and second sidewalls 26 b, 26 c.

According to the battery of the first embodiment explained above, theleads, the current-collecting tabs of the wound electrode group, and theouter can are prevented from coming into contact with each other, andwhen the lead and the current-collecting tab or the fixing member aredisconnected due to vibration, shock, or the like, the lead is preventedfrom coming into contact with the wound electrode group and causingshort circuit. Therefore, the highly safe sealed secondary battery canbe provided.

It should be noted that the insulating cover having the above shape isnot limited to the negative electrode insulating cover. It may be usedas the positive electrode insulating cover.

(Second embodiment)

The battery according to the second embodiment has the sameconfiguration as the first embodiment except for change in the shape ofthe insulating cover. FIG. 11 illustrates a negative electrodeinsulating cover 31 used in the present embodiment. In the explanationbelow, the negative electrode insulating cover is explained as anexample. However, the positive electrode insulating cover also has thesame shape and is arranged symmetrically with the negative electrodeinsulating cover.

In the present embodiment, the insulating cover 31 comprises a U-shapedmember 31 a, a back surface member 31 d, and a sandwiching member. TheU-shaped member 31 a has first and second sidewalls 31 b, 31 c facingeach other. The back surface member 31 d is integrated with the backsurface of the U-shaped member 31 a. The sandwiching member sandwichesthe negative electrode current-collecting tab 9 a and the first andsecond sandwiching strips 4 c, 4 d of the negative electrode-lead 4. Alower portion of the U-shaped member 31 a is bent, and an upper portionthereof is open. The U-shaped member 31 a is made such that the sideopposite to the back surface member 31 d is also open.

The sidewalls 31 b, 31 c arranged to face each other in the U-shapedmember 31 a are bent to the outside about 180 degrees. First and secondthick portions 31 e, 31 f are formed by those sidewalls 31 b, 31 c.Accordingly, the thick portions 31 e, 31 f are provided on thesubstantially entire length of the insulating cover 31 in the verticaldirection.

The back surface member 31 d has a rectangular protruding portion 31 g.The protruding portion 31 g is provided with predetermined clearances (afirst clearance 31 x, a second clearance 31 y) respectively between thefirst and second thick portions 31 e, 31 f. The length of protrusion ofthe protruding portion 31 g from the back surface member 31 d is lessthan the width of the U-shaped member 31 a. In this case, the width ofthe U-shaped member 31 a means a length from the back surface member 31d to the end portions at the electrode group side in the sidewalls 31 b,31 c. The protruding portion 31 g is provided at the same height as thefixing member 12 attached to the current-collecting tab of the woundelectrode group 2. For example, the protruding portion 31 g has a shapeof a square pole in which corners in a longitudinal direction arechamfered. It should be noted that the protruding portion 31 g may be ina hollow shape.

The sandwiching member comprises these first and second thick portions31 e, 31 f and the protruding portion 31 g.

In the thick portions 31 e, 31 f, a length (L′) of the insulating cover31 in the vertical direction is longer than a length (L) of the fixingmember 12. Therefore, the thick portions 31 e, 31 f of the sandwichingmember can hold not only the joint portion between the sandwichingstrips 4 c, 4 d of the negative electrode-lead 4 and the couplingportions 12 a, 12 b of the fixing member 12 but also the sandwichingstrips 4 c, 4 d above the joint portion and the negative electrodecurrent-collecting tab 9 a below the joint portion. Therefore, the jointportion between the sandwiching strips of the lead and the fixing membercan be held more rigidly. Moreover, the insulating cover 31 is lesslikely to be detached.

According to the battery using the insulating covers having the shape asdescribed above, the insulating covers are less likely to be detachedfrom the wound electrode group 2, and the joint portion between thesandwiching strips of the lead and the fixing member can be held morerigidly. Therefore, the highly safe sealed secondary battery can beprovided.

Subsequently, a first modification of the insulating cover will be shownin FIG. 12. The insulating cover 31 as shown in FIG. 12 has an extendingportion 31 h provided at a bent portion of a lower of a U-shaped member31 a, and the extending portion 31 h extends in a direction opposite tothe back surface member 31 d. Further, the extending portion 31 h hasone or more channel grooves 31 i extending in parallel with theextending portion 31 h.

Since the wound electrode group 2 is held by the extending portion 31 h,the insulating cover 31 according to the first modification is fixed tothe wound electrode group 2 more rigidly. Further, the channel grooves31 i also function as inflow paths of electrolyte. When the woundelectrode group 2 is accommodated in the outer can 1, and theelectrolyte is injected, the electrolyte flows into the wound electrodegroup 2 via the channel grooves 31 i. This accelerates impregnation ofthe electrolyte into the wound electrode group 2.

Subsequently, a second modification of the insulating cover will beshown in FIG. 13. In the insulating cover 31 as shown in FIG. 13, theprotruding portion 31 g has three penetrating holes 31 j penetratingfrom the outside of the back surface member 31 d to the surface at theside of the wound electrode group. For example, the penetrating holes 31j are arranged at regular intervals on the surface of the protrudingportion 31 g.

Since the penetrating holes 31 j exist in the protruding portion 31 g,this accelerates flow of the electrolyte into the inside of theinsulating cover 31. This accelerates impregnation of the electrolyte.Therefore, the productivity of the batteries can be improved. Inaddition, gases leaked out of the inside of the wound electrode groupcan be smoothly moved to the outside of the insulating cover 31. Thisprevents the insulating cover 31 from being detached by the gaspressure.

In FIG. 13, the three penetrating holes 31 j are arranged at regularintervals, but the arrangement is not limited thereto. At least onepenetrating hole may be arranged. Alternatively, in a case where aplurality of penetrating holes are arranged, they are not required to bearranged at regular intervals, and each may be arranged at any position.The protruding portion 31 g having the penetrating holes may be formedby forming the insulating cover by stamping mold.

Subsequently, a third modification of the insulating cover will be shownin FIG. 14. The insulating cover 31 as shown in FIG. 14 has an extendingportion 31 h provided at a bent portion of a lower of a U-shaped member31 a, and the extending portion 31 h extends in a direction opposite tothe back surface member 31 d. The extending portion 31 h has one or morechannel grooves 31 i extending in parallel with the extending portion 31h. The protruding portion 31 g has three penetrating holes 31 jpenetrating from the outside of the back surface member 31 d to thesurface at the side of the wound electrode group. For example, thepenetrating holes 31 j are arranged at regular intervals on the surfaceof the protruding portion 31 g.

Since the wound electrode group 2 is held by the extending portion 31 h,the insulating cover 31 according to the third modification is fixed tothe wound electrode group 2 more rigidly. Further, the channel grooves31 i also function as inflow paths of electrolyte. When the woundelectrode group 2 is accommodated in the outer can 1, and theelectrolyte is injected, the electrolyte flows into the wound electrodegroup 2 via the channel grooves 31 i. This accelerates impregnation ofthe electrolyte into the wound electrode group 2. Since the penetratingholes 31 j exist in the protruding portion 31 g, this accelerates flowof the electrolyte into the inside of the insulating cover 31. Thisaccelerates impregnation of the electrolyte. Therefore, the productivityof the batteries can be improved. In addition, gases leaked out of theinside of the wound electrode group can be smoothly moved to the outsideof the insulating cover 31. This prevents the insulating cover 31 frombeing detached by the gas pressure.

Subsequently, a fourth modification of the insulating cover will beshown in FIG. 15. In the insulating cover 31 as shown in FIG. 15, theprotruding portion 31 g has a central portion 31 k, an upper portion 31Lin a pyramid shape, and a lower portion 31 m in an inverted-pyramidshape. The central portion 31 k, the upper portion 31L, and the lowerportion 31 m respectively have penetrating holes 31 j ₁, 31 j ₂, and 31j ₃ penetrating from the outside of the back surface member 31 d to thesurface at the side of the wound electrode group.

Since the protruding portion 31 g has the lower portion 31 n in theinverted-pyramid shape, and the lower portion 31 n has the penetratinghole 31 j ₃, the electrolyte smoothly flows into the inside of theinsulating cover 31. Therefore, the wound electrode group can be quicklyimpregnated with the electrolyte. Therefore, the productivity of thebatteries can be improved. The upper portion 31L in the pyramid shapemakes a clearance between the protruding portion 31 g and the fixingmember, and gases leaked out of the inside of the wound electrode groupcan be more smoothly moved from the penetrating hole 31 j ₂ of the upperportion 31L to the outside of the insulating cover. This prevents theinsulating cover 31 from being detached by the gas pressure.

It should be noted that the shape of the upper portion 31L is notlimited to the pyramid shape, and may be formed in any shape. The shapeof the lower portion 31 m is not limited to the inverted-pyramid shape,and may be in any shape as long as the lower is tapered toward the end.

Each of the central portion 31 k, the upper portion 31L, and the lowerportion 31 m has one penetrating hole 31 j, but each may have aplurality of penetrating holes.

Subsequently, a fifth modification of the insulating cover will be shownin FIG. 16. The insulating cover 31 as shown in FIG. 16 has an extendingportion 31 h provided at a bent portion of a lower of a U-shaped member31 a, and the extending portion 31 h extends in a direction opposite tothe back surface member 31 d. The extending portion 31 h has one or morechannel grooves 31 i extending in parallel with the extending portion 31h. The protruding portion 31 g has a central portion 31 k, an upperportion 31L in a pyramid shape, and a lower portion 31 m in aninverted-pyramid shape. The central portion 31 k, the upper portion 31L,and the lower portion 31 m respectively have penetrating holes 31 j ₁,31 j ₂, and 31 j ₃ penetrating from the outside of the back surfacemember 31 d to the surface at the side of the wound electrode group.

Since the wound electrode group 2 is held by the extending portion 31 h,the insulating cover 31 according to the fifth modification is fixed tothe wound electrode group 2 more rigidly. Further, the channel grooves31 i also function as inflow paths of electrolyte. When the woundelectrode group 2 is accommodated in the outer can 1, and theelectrolyte is injected, the electrolyte flows into the wound electrodegroup 2 via the channel grooves 31 i. This accelerates impregnation ofthe electrolyte into the wound electrode group 2.

Since the protruding portion 31 g has the lower portion 31 n in theinverted-pyramid shape, and the lower portion 31 n has the penetratinghole 31 j ₃, the electrolyte smoothly flows into the inside of theinsulating cover 31. Therefore, the wound electrode group can be quicklyimpregnated with the electrolyte. Therefore, the productivity of thebatteries can be improved. The upper portion 31L in the pyramid shapemakes a clearance between the protruding portion 31 g and the fixingmember, and gases leaked out of the inside of the wound electrode groupcan be more smoothly moved from the penetrating hole 31 j ₂ of the upperportion 31L to the outside of the insulating cover. This prevents theinsulating cover 31 from being detached by the gas pressure.

In the battery according to the present embodiment, the insulating coverhaving the same shape as the insulating cover at the negative electrodemay be attached to the positive electrode of the wound electrode group2, or an insulating cover having a different shape may be attachedthereto.

(Third embodiment)

A battery according to the third embodiment will be described withreference to FIGS. 17 and 18. The battery of the third embodiment has asimilar configuration to that of the first embodiment except that theshapes of the positive/negative electrode-leads and thepositive/negative electrode insulating cover differ from those describedabove. In the descriptions below, the same reference numerals or symbolsas used above will be used to indicate similar or correspondingstructural elements, and a detailed description of such elements will beomitted.

A positive electrode-lead 3′ comprises: a connection plate 3′a servingas a connection portion connected to a positive electrode terminal 6; apenetrating hole 3′b formed in the connection plate 3′a; and anextending portion 3′c extending from the connection plate 3′a toward awound electrode group 2 in a direction perpendicular to the winding axisof the wound electrode group 2 and connected to a wound positiveelectrode current-collecting tab 8 a.

A negative electrode-lead 4′ comprises: a connection plate 4′a servingas a connection portion connected to a negative electrode terminal 7; apenetrating hole 4′b formed in the connection plate 4′a; and anextending portion 4′c extending from the connection plate 4′a toward thewound electrode group 2 in a direction perpendicular to the winding axisof the wound electrode group 2 and connected to a wound negativeelectrode current-collecting tab 9 a.

A positive electrode insulating cover 32 comprises: a U-shaped member 32a that has first and second sidewalls 32 b, 32 c facing each other, aback surface member 32 d, and a sandwiching member configured tosandwich a positive electrode current-collecting tab 8 a and theextending portion 3′c of the positive electrode-lead connected thereto.The sandwiching member comprises rectangular thick portions 32 e and 32f provided at the first and second sidewalls 32 b and 32 c facing eachother.

In the positive electrode insulating cover 32 of the aboveconfiguration, thick portion 32 e is in contact with the extendingportion 3′c of the positive electrode-lead 3′c, which engages with thepositive electrode current-collecting tab 8 a. On the other hand, thickportion 32 f is in contact with the first holding unit 11 a of a fixingmember 11. Therefore, the positive electrode current-collecting tab 8 aand the extending portion 3′c of the positive electrode-lead aresandwiched between thick portions 32 e and 32 f. Since the extendingportion 3′c of the positive electrode-lead is located on only one sideof the positive electrode current-collecting tab 8 a, thick portion 32 emay be thinner than thick portion 32 f.

A negative electrode insulating cover 33 has a similar configuration tothat of the positive electrode insulating cover and is arranged insymmetric thereto.

The positive and negative electrode-leads having the above configurationare light in weight, and do not occupy much volume inside the outer can.This feature contributes to the reduction of the weight of the batteryand to high energy density.

FIG. 18 shows a modification of the positive electrode insulating coverused in the third embodiment. The insulating cover 32 comprises arectangular protruding portion 32 g provided on the back surface member32 d. The protruding portion 32 g is located between thick portions 32 eand 32 f, and the length from the back surface member 32 d to a surfaceopposite thereto is less than the width of the sidewalls 32 b, 32 c ofthe U-shaped member. The sandwiching member comprises the first andsecond thick portions 32 e and 32 f as well as the protruding portion 32g.

The protruding portion 32 g may have a penetration hole, as described inconnection with the second embodiment.

As described in connection with the second embodiment, the positiveelectrode insulating cover may be modified such that the first andsecond sidewalls of the U-shaped member may be bent outwardly. In thiscase, the sandwiching member of the positive electrode insulating covercomprises the bent portions of the sidewalls. Furthermore, the positiveelectrode insulating cover may comprise a bent sidewall and arectangular protruding portion provided on the back surface member. Inthis case, the sandwiching member comprises the bent portion of thesidewalls and the protruding portion.

The insulating cover used in the embodiment may be designed such thatthe U-shaped member comprises an extending portion that extends from thebent portion in a direction opposite to the back surface member.

The above description was given, referring to the positive electrodeinsulating cover. Needless to say, the negative electrode insulatingcover may have a similar shape to that of the positive electrodeinsulating cover, and may be arranged to be symmetric with respect tothe positive electrode insulating cover.

(Positive/negative Electrode Terminals)

Materials of positive/negative electrode terminals that can be used inthe battery according to the first to the third embodiments will beexplained. In a case of a lithium ion secondary battery in whichcarbon-based materials are used as negative electrode active materials,aluminum or aluminum alloy is usually used as a material for thepositive electrode terminal. In addition, metal such as copper, nickel,and nickel-plated iron are used as materials for the negative electrodeterminal. In a case where a lithium titanate is used as a negativeelectrode active material, not only the above materials but alsoaluminum or aluminum alloy may be used as materials for the negativeelectrode terminal. When aluminum or aluminum alloy is used for thepositive/negative electrode terminals, the positive/negative electrodecurrent-collecting tabs, the positive/negative electrode fixing members,and the positive/negative electrode-leads are preferably made ofaluminum or aluminum alloy.

(Positive Electrode)

Subsequently, a positive electrode that can be used in the batteryaccording to the first to the third embodiments will be explained.

For example, the positive electrode is made by applying slurrycontaining positive electrode active materials to a current-collectingbody made of aluminum foil or aluminum alloy foil and drying the slurry.The positive electrode active materials are not particularly limited.For example, oxides, sulfides, and polymers capable of absorbing andreleasing lithium can be used as the positive electrode activematerials. Examples of preferred active materials include lithiummanganese oxide compound, lithium nickel composite oxide, lithium cobaltcomplex oxide, and lithium iron phosphate, which are capable ofproviding high positive electrode potential.

(Negative Electrode)

Subsequently, a negative electrode that can be used in the batteryaccording to the first to the third embodiments will be explained.

For example, the negative electrode is made by applying slurrycontaining negative electrode active materials to a current-collectingbody made of aluminum foil or aluminum alloy foil and drying the slurry.The negative electrode active materials are not particularly limited.For example, metal oxides, metal sulfides, metal nitrides, and alloyscapable of absorbing and releasing lithium can be used as the negativeelectrode active materials. Materials having a lithium ion absorbing andreleasing potential nobler by 0.4 V or more than the metal lithiumpotential are preferably used. Negative electrode active materialshaving such a lithium ion absorbing and releasing potential suppress areaction between aluminum or an aluminum alloy and lithium, whichenables aluminum or an aluminum alloy to be used for the negativeelectrode current-collecting body and structural members related to thenegative electrode. Examples of the negative electrode active materialinclude titanium oxides, lithium-titanium complex oxides such as lithiumtitanate, tungsten oxides, amorphous tin oxides, tin-silicon oxides andsilicon oxides, and among these compounds, lithium-titanium complexoxides are preferable.

(Separator)

Subsequently, a separator that can be used in the battery according tothe first to the third embodiments will be explained. As the separator,microporous membranes, woven fabrics, and nonwoven fabrics orcombinations of two or more of these materials may be used. Thelaminated material may be made of the same material or differentmaterials. Examples of the material used to form the separator mayinclude polyethylene, polypropylene, ethylene/propylene copolymer, andethylene/butene copolymer.

(Electrolyte)

Subsequently, an electrolyte that can be used in the battery accordingto the first to the third embodiments will be explained.

A non-aqueous electrolyte solution prepared by dissolving an electrolyte(for example, lithium salt) in a non-aqueous solvent is used as anelectrolyte. Examples of a non-aqueous solvents include ethylenecarbonate (EC), propylene carbonate (PC), butylene carbonate (BC),dimethle carbonate (DMC), dietyle carbonate (DEC), ethyl methylcarbonate (EMC), gamma-butyro lactone (gamma-BL), sulfolane,acetonitrile, 1,2-dimethoxy ethane, 1,3-dimethoxy propane, dimethylether, a tetra-hydro franc (THF), and a 2-methyl tetra-hydro franc. Thenon-aqueous solvent may be used independently, or two or more solventsmay be mixed.

Examples of electrolytes include lithium salts such as lithiumperchlorate (LiClO₄), 6-fluoridation perphosphoric acid lithium (LiPF₆),4-fluoridation-lithium-borate (LiBF₄), 6-fluoridation-arsenic lithium(LiAsF₆), and trifluoro-meta-sulfonic acid lithium (LiCF₃SO₃). Theelectrolyte may be used independently, or two or more electrolytes maybe mixed. The electrolyte amount of dissolutions to an electrolyticnon-aqueous solvent is preferably set to 0.2 mol/L to 3 mol/L.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A battery comprising: a metallic outer can; awound electrode group accommodated in the outer can in a directionperpendicular to a winding axis, wherein a wound positive electrodecurrent-collecting tab is provided at one end of the wound electrodegroup, and a wound negative electrode current-collecting tab is providedat the other end of the wound electrode group; a positive electrode-leadconnected to the positive electrode current-collecting tab; a negativeelectrode-lead connected to the negative electrode current-collectingtab; a metallic lid comprising a positive electrode terminal and anegative electrode terminal and being attached to an opening portion ofthe outer can; a positive electrode insulating cover engaged with oneend portion including the positive electrode current-collecting tab ofthe wound electrode group; and a negative electrode insulating coverengaged with the other end portion including the negative electrodecurrent-collecting tab of the wound electrode group, wherein thepositive electrode-lead comprises a connection portion connected to thepositive electrode terminal and first and second extending portions thatextend from the connection portion to the wound electrode group in thedirection perpendicular to the winding axis to sandwich the woundpositive electrode current-collecting tab, the negative electrode-leadcomprises a connection portion connected to the negative electrodeterminal and first and second extending portions that extend from theconnection portion to the wound electrode group in the directionperpendicular to the winding axis to sandwich the wound negativeelectrode current-collecting tab, the positive electrode insulatingcover comprises a first U-shaped member, the first U-shaped memberincluding first and second sidewall portions extending in the directionperpendicular to the winding axis and facing each other with thepositive electrode current-collecting tab and the first and secondextending portions of the positive electrode-lead interposedtherebetween, a back surface portion extending in the directionperpendicular to the winding axis and facing the negative electrodeinsulating cover with the wound electrode group interposed therebetween,a bent lower portion extending between lower ends of the first andsecond sidewall portions of the first U-shaped member such that the bentlower portion of the first U-shaped member is convex downward, and anextending portion extending from the bent lower portion of the firstU-shaped member such that the extending portion of the first U-shapedmember protrudes with respect to the first and second sidewall portionsof the first U-shaped member toward the negative electrode insulatingcover, and the negative electrode insulating cover comprises a secondU-shaped member, the second U-shaped member including first and secondsidewall portions extending in the direction perpendicular to thewinding axis and facing each other with the negative electrodecurrent-collecting tab and the first and second extending portions ofthe negative electrode-lead interposed therebetween, a back surfaceportion extending in the direction perpendicular to the winding axis andfacing the positive electrode insulating cover with the wound electrodegroup interposed therebetween, a bent lower portion extending betweenlower ends of the first and second sidewall portions of the secondU-shaped member such that the bent lower portion of the second U-shapedmember is convex downward, and an extending portion extending from thebent lower portion of the second U-shaped member such that the extendingportion of the second U-shaped member protrudes with respect to thefirst and second sidewall portions of the second U-shaped member towardthe positive electrode insulating cover.
 2. The battery according toclaim 1, wherein the positive electrode insulating cover and thenegative electrode insulating cover comprise: a rectangular portionprovided on each of the first and second sidewalls facing each other. 3.The battery according to claim 2, further comprising: a rectangularprotruding portion provided on the back surface member, wherein theprotruding portion is located between the rectangular portions, and alength from the back surface member to a surface opposite thereto isless than a width of the sidewall of the first and second U-shapedmembers.
 4. The battery according to claim 3, wherein the protrudingportion comprises a penetrating hole.
 5. The battery according to claim1, wherein the first and second sidewalls, which face each other, of theU-shaped member of each of the positive electrode insulating cover andthe negative electrode insulating cover are bent outwardly, the positiveelectrode insulating cover and the negative electrode insulating covercomprise bent sidewalls.
 6. The battery according to claim 5, whereinthe positive electrode insulating cover and the negative electrodeinsulating cover comprise bent sidewalls and a rectangular protrudingportion provided on the back surface member, and the protruding portionis located between the bent sidewalls, and a length from the backsurface member to a surface opposite thereto is less than a width of thesidewall of the first and second U-shaped members.
 7. The batteryaccording to claim 6, wherein the protruding portion comprises apenetrating hole.
 8. The battery according to claim 1, wherein theextending portion comprises a channel groove that extends in parallelwith the extending portion.
 9. The battery according to claim 2, furthercomprising: a rectangular protruding portion provided on the backsurface member, wherein the rectangular protruding portion is locatedbetween the rectangular portions and is inserted into the woundelectrode group.
 10. The battery according to claim 5, wherein thepositive electrode insulating cover and the negative electrodeinsulating cover comprise bent sidewalls and a rectangular protrudingportion provided on the back surface member, and the rectangularprotruding portion is located between the bent sidewalls and is insertedinto the wound electrode group.